Delayed evacuatory function due to specific smooth muscle reactivity in the gastrointestinal tracts of tacrine-treated rats.

Most of the side effects induced by tacrine are associated with the gastrointestinal (GI) tract. The aim of the study was to analyze the nature of radiographically registered, tacrine-induced changes in evacuatory function, as well as to find a possible correlation with the immediate in vitro action of the drug on smooth muscles from the GI tracts of rats. The tacrine dose we used reliably delayed GI passage: contrast matter was not fully evacuated, predominantly from the stomach and cecum. The delay resulted from changes in tone and peristaltic activity, specific for the various regions of the tract. These changes were associated with a superposing of the responses due to the anticholinesterase and noncholinergic action of tacrine.

Effects of high-affinity GABAB receptor antagonists on active and passive avoidance responding in rodents with gamma-hydroxybutyrolactone-induced absence syndrome.

RATIONALE: Absence seizures in man are behaviourally manifested as arrest and mild jerks mainly of facial muscles, associated in the electroencephalogram with synchronous spike and wave discharges. Gamma-hydroxybutyrolactone (GHBL) administration is currently used as an experimental model of absence seizures in rats and mice. OBJECTIVE: The aim of the present study was to examine the effects of three potent gamma-aminobutyric acid (GABA)B receptor antagonists CGP55845A, CGP62349 and CGP71982 (0.01 mg/kg) on the development of GHBL-induced absence epilepsy and in learning paradigms of active and passive avoidance tests in GHBL-treated mice and rats. METHODS: After 4 weeks of development of the absence syndrome, active and passive avoidance tests with negative reinforcement were performed. In both animal species, the absence syndrome was observed after 3 weeks of treatment in the saline group. RESULTS: The GABAB receptor antagonists CGP55845A and CGP62349 appeared to suppress the development of the absence syndrome to a greater degree in mice than in rats. CGP71982 suppressed it later than the other two antagonists (fifth week). In an active avoidance test in GHBL-treated mice, the GABAB antagonists had different effects - CGP62349 improved learning and memory retention to a greater extent than CGP55845A, whilst CGP71982 had no influence on it. In a passive avoidance test in GHBL-treated mice, the GABAB antagonists also had different effects - CGP71982 improved both learning and memory retrieval, whereas CGP55845A and CGP62349 had no effect. In the active avoidance test in GHBL-treated rats, the GABAB antagonist CGP55845A improved learning, whereas the other two, CGP62349 and CGP71982, had no effect. In the passive avoidance test the GHBL-treated rats showed an improvement in short memory retrieval. CGP55845A and CGP71982 improved this further, whilst CGP62349 had no effect. CONCLUSIONS: GHBL appeared to influence mice and rats in a different manner - rats learned the active avoidance task better than the GHBL-treated mice. The present study confirms previous data that GABAB antagonists suppress absence behaviour.

The modulatory effects of high affinity GABA(B) receptor antagonists in an active avoidance learning paradigm in rats.

It has been reported that selective GABA(B) receptor antagonists can enhance cognitive performance in a variety of learning paradigms. This prompted us to examine the effects of some more potent and newly synthesised GABAB antagonists CGP 71982, CGP 62349 and CGP 55845A in an active avoidance test in rats. A two-way active avoidance test with negative reinforcement was performed for the first 5 of 12 days of antagonist administration. CGP 71982 and CGP 55845A at all doses applied (0.01-1.0 mg/kg) had an improving effect on learning, and memory retention on day 12; the rats made more avoidances in both sessions compared to controls. CGP 62349 was only active at the lowest dose tested (0.01 mg/kg). The present study confirms that GABA(B) receptor antagonists can enhance cognitive performance but provides no insight into the mechanism of action of these novel antagonists.

Effects of GABAB receptor antagonism on the development of pentylenetetrazol-induced kindling in mice.

Pentylenetetrazol (PTZ) administered chronically in rodents induces kindling which is considered to be a model of chronic epilepsy mediated through a specific interaction with the GABA-gated chloride ionophore. PTZ kindling also impairs shuttle-box learning indicating a possible modulation of memory storage [A. Becker, G. Grecksch, H. Mathies. The influence of diazepam on learning processes impaired by pentylenetetrazol kindling. Naunyn-Schmiedeberg's Arch. Pharmacol. 349 (1994) 429-496]. Since GABAB receptor antagonism has been shown to improve cognitive performance in rodents and primates we have examined the effects of 3 antagonists; CGP 36742 (3-amino-propyl-n-butyl-phosphinic acid), CGP 56433 ([3-¿1-(S)-[¿3-(cyclohexylmethyl) hydroxyphosphinyl]-2-(S)-hydroxypropyl]-amino]ethyl]benzoic acid) and CGP 61334 ([3-¿[3[(diethoxymethyl)hydroxyphosphinyl]-propyl-amino¿meth yl]-benzoic acid) on the induction of PTZ kindling in mice at 48 h intervals for 8 weeks. Subsequently the mice were tested in an active avoidance paradigm. At the end of the experiment GABAB receptor autoradiography was performed on brain sections from these animals. Seizure intensity increased progressively in control mice reaching by 8 weeks a mean score which corresponded to clonic seizures. The GABAB antagonists suppressed kindling during the first 4 weeks and after that restored the seizure intensity to the level of control animals. The level of kindling was proportional to the avoidance score. The density of GABAB receptor binding in brain sections from PTZ kindled mice was significantly greater than in controls. This was not altered by pretreatment with the GABAB antagonists except in the cerebellum.

Effects of GABAB receptor antagonists on learning and memory retention in a rat model of absence epilepsy.

A variety of animal models of absence epilepsy have been described and among these exists a genetically susceptible strain of rat (genetic absence epilepsy rats of Strasbourg (GAERS)). These rats produce periods of behavioural arrest with simultaneous production of cortical spike and wave discharges (SWD). GABAB receptor antagonists suppress completely the production of these spike and wave discharges. GABAB receptor ligands have also been reported to affect cognitive performance in rodents. The present study examined the cognitive performance of GAERS and the influence of GABAB receptor antagonists on this activity. Rats were injected intraperitoneally once per day with saline or a GABAB receptor antagonist (CGP 36742 (3-amino-propyl-n-butyl-phosphinic acid) 100 mg/kg; CGP 56433 ([3-(1-(S)-[(3-(cyclohexylmethyl)hydroxy phosphinyl]-2-(S) hydroxy propyl] amino]ethyl]benzoic acid) ([3-{1-(S)-[{3-(cyclohexylmethyl)hydroxy phosphinyl]-2-(S) hydroxy propyl] amino]ethyl]benzoic acid) 1 mg/kg or CGP 61334 ([3-({[3-[(diethoxymethyl)hydroxy phosphinyl]propyl] amino}methyl]-benzoic acid (1 mg/kg). A two-way active avoidance test paradigm with negative reinforcement was used. Untreated GAERS performed significantly better than non-epileptic rats (P < 0.05) and this enhancement in cognitive performance was sustained in rats treated with the GABAB receptor antagonists.

Effects of GABA(B) receptor antagonists on spontaneous and on GABA-induced mechanical activity of guinea-pig smooth muscle preparations.

The majority of GABA(B) receptor antagonists have been based on alterations of the acidic moiety of gamma-aminobutyric acid (GABA) or baclofen, such as the first selective antagonist phaclofen. More recently, a new structural class of compounds derived by p-alkyl substitution in the phosphinic analog of GABA, such as CGP35348 (3-amino-propyl-(diethoxymethyl)-phosphinic acid), have been introduced as GABA(B) receptor antagonists. The present study examine the influence of a series of structurally related phosphinic acid analogues on mechanical activity and their effect on GABA-induced reactions in ileal smooth muscle. In our experiments, GABA exerted a biphasic contractile-relaxation effect with pronounced dose-dependent characteristics. 3-[[1-(S)-(3,4-Dihydrophenyl) ethyl]amino]-2-(S)-hydroxy-propyl]-(phenylmethyl)-phosphinic acid hydrochloride (CGP55845A) induced prolonged relaxation without changing the phasic activity of the ileum preparations. [3-[1-R-[[2-(S)-hydroxy-3-[hydroxy-4-methoxyphenyl]-methyl]-phosphinyl]-propyl]-aminoethyl]-benzoic acid (CGP62349) did not change the mechanical activity of smooth muscle preparation. Trans 3-[6-[[Cyclo hexylmethyl-hydroxy-phosphinyl]-methyl]-3-morpholinyl]-benzoic acid (CGP71982) itself induced smooth muscle contractions. GABA(B) receptor antagonists decreased concentration-dependently the relaxation phase of the action of GABA from 50% to 90%. Their effect on the contractile phase of the action of GABA was quite different-CGP55845A decreased it dose-dependently, whereas CGP62349 and CGP71982 did not change it significantly. These findings prompted us to assume that the GABA(B) receptor antagonists studied, being phosphinic analogues, probably act on GABA(B) receptors in guinea-pig ileum smooth muscles.

Effects of angiotensin II on brain monoamines in nonhypoxic and hypoxic mice.

The effects of angiotensin II (ATII) administered intracerebroventricularly (ICV, acute) and subcutaneously (SC, acute and chronic) on acute hypoxia (asphyctic and hemic), and on the forebrain concentrations of monoamines dopamine (DA), norepinephrine (NE), and serotonin (5-HT) in male mice were studied. ATII in both routes of administration exerted a decrease of the latency to hypoxia-induced convulsions. ATII slightly reduced the brain levels of DA and NE, and did not change those of 5-HT in hypoxic mice. ATII significantly reduced DA and 5-HT concentrations in nonhypoxic (normoxic) mice. Taken together, the results suggest that ATII-induced increase of susceptibility to hypoxia is accompanied by slight alterations in the brain monoamine metabolism.

Determination of carbamazepine and its metabolite carbamazepine-10,11-epoxide in serum with gas-chromatography mass spectrometry.

Carbamazepine, one of the most often used antiepileptic drugs, undergoes enzyme biotransformation through epoxidation with the formation of its metabolite, carbamazepine-10,11-epoxide (carbamazepine epoxide). The determination of carbamazepine epoxide is clinically significant in therapeutic drug monitoring as it decreases the risk of toxic reactions and increases the possibility of reaching the expected therapeutic result. The aim of this study was to introduce a gas chromatographic method with mass spectrometric detection to simultaneously determine the serum levels of carbamazepine and carbamazepine epoxide. Blood samples from 80 epileptic patients aged between 1 and 63 years were analyzed. All patients were taking carbamazepine as monotherapy and had achieved the steady state serum drug concentration. A microcolumn extraction of carbamazepine and carbamazepine epoxide was obtained by elution. A gas chromatograph with a mass spectrometer and a 25 m x 0.2 mm ID, 0.33 micron film thickness, crosslinked 5% phenyl-methylsilicone capillary column HP-5 was used. The coefficients of correlation for the calibration plots obtained for carbamazepine epoxide and carbamazepine were 0.988 and 0.995, respectively. The precision, tested for n = 20, showed coefficients of variation within one day as follows: carbamazepine epoxide: 11.0% and 6.55%; carbamazepine: 11.8% and 5.4%. The coefficients of variation from day to day were: carbamazepine epoxide: 9.4% and 6.83%; carbamazepine: 8.5% and 5.7%. The detection limit was 10 micrograms/l and the recovery 82.5% for carbamazepine epoxide and 92.5% for carbamazepine. A fast and simple gas chromatographic method for the routine therapeutic monitoring of carbamazepine and carbamazepine epoxide was developed. The simultaneous determination of the serum levels of carbamazepine epoxide and carbamazepine offers the possibility of measuring the total drug concentration, as well as that of its metabolite, while considering the results of clinical response and the special features of carbamazepine's enzymatic biotransformation through epoxidation with the formation of its metabolite.

Effect of elymoclavine on open field behaviour of rats and pharmacological analysis of its catecholaminergic mechanisms.

The effect of elymoclavine on rat open field behaviour was examined. The participation of catecholaminergic mechanisms in the elymoclavine effect on rat open field behaviour was also studied using pharmacological tools for analyzing these mechanisms. Elymoclavine in increasing doses stimulated ambulation and rearing but inhibited defecation. Haloperidol blocked the responses to all doses of elymoclavine. The effect of elymoclavine on ambulation was potentiated by propranolol, desipramine and pargyline. Its effect on rearing was reduced by desipramine, pargyline, alpha-methyl-p-tyrosine (alpha-MpT), L-DOPA, DDC (diethyldithiocarbamate) and 6-OHDA (applied intracerebroventricularly). The effect of elymoclavine on defecation was reduced only by DDC. It is concluded that elymoclavine influences both locomotor components of exploratory behaviour in the open field (ambulation and rearing) and defecation. These behavioural effects of elymoclavine are realized through the participation of central catecholaminergic mechanisms (dopaminergic and to a less extent noradrenergic).

Anticonvulsive effect of 2-hydroxylamine-5-ethyl-5-sec-pentyl barbituric acid (HB-7) in two experimental models of epilepsy.

The effects of barbiturate HB-7 (2-hydroxylamine-5-ethyl-5-sec-pentylbarbituric acid) injected intraperitoneally compared to the effects of pentobarbital and/or phenobarbital were investigated in three series of experiments on cats: normal electrocorticogram (ECoG); pentylentetrazol-induced generalized paroxysmal ECoG; and paroxysmal ECoG activity induced by topical application of penicillin on the exposed cortical surface. In the first series, HB-7 led to the appearance of ECoG spindles of the same type as those elicited by pentobarbital. In the second series (pentylentetrazol-treated group), HB-7 increased the two thresholds: one associated with the appearance of isolated paroxysmal spike-wave complexes and the other corresponding to the appearance of generalized paroxysmal ECoG activity. In the third series, HB-7 led to an inhibition of penicillin spikes, both in the focus itself and in the other cortical areas where they propagated. The possibility for using HB-7 as an antiepileptic drug was discussed.

Mechanisms of the angiotensin II effects on exploratory behavior of rats in open field. III. Modulatory role of GABA.

The effects of the octapeptide angiotensin II (AT II) and its interactions with GABA (gamma-aminobutyric acid) on the exploratory behavior of male rats in open field were studied. AT II (0.1 and 0.5 microgram i.c.v.) increased the open field behavior, mainly ambulation and rearing. GABA (100 micrograms i.c.v.) significantly reduced the effects of AT II. This influence of GABA was potentiated by subconvulsive doses of bicuculline. Our results demonstrate that the GABAergic system exerts an inhibitory control on pathways mediating the stimulatory effects of AT II on exploratory behavior in open field. The data also suggest close interactions between GABA AT II receptors.

Effects of the antidepressant drug moclobemide on learning and memory in rats.

Moclobemide is a well known drug with antidepressant action. The aim of this study was to investigate the effects of moclobemide on learning and memory processes in Sprague Dawley rats. Over a 5-day period, learning sessions with 30 trials per day and memory retention tests were performed. The conditioned responses (avoidances), the unconditioned responses (escapes) and the intertrial crossings were observed. An active avoidance test was carried out using a shuttle box. Two passive avoidance tests were used: step-through (using a light chamber) and step-down (using a platform). In the step-through passive avoidance test, the learning and retention sessions consisted of three trials each and the latency of reaction times (the rat remaining in the light chamber for more than 180 sec) was used as criterion. In the step-down passive avoidance test, learning and retention sessions consisted of two trials and the latency of reaction times (the rat remaining on the platform for 60 sec) was used as criterion. In the active avoidance tests, moclobemide dose-dependently increased the number of avoidances during learning sessions and maintained this number in memory retention tests. Moclobemide did not alter the number of escapes, but did increase motor activity. In the passive avoidance tests, moclobemide also increased the latency of reaction times in learning and short memory retrieval tests. These findings suggest that moclobemide improves learning and memory processes in active and passive avoidance tests and has a cognition-enhancing effect.

Mechanisms of the angiotensin II effects on the exploratory behavior of rats in open field. I. Interaction of angiotensin II with saralasin and catecholaminergic drugs.

The effects of the octapeptide angiotensin II (AT II) and its possible interaction with catecholaminergic (mainly dopaminergic) neurotransmission on the exploratory behavior of male rats in open field were studied. AT II changed exploratory behavior in a nonlinear dose-effect manner. The stimulant effects of AT II were antagonized by the AT II receptor antagonist saralasin. The AT II effects were increased by the DAergic agonists apomorphine and nomifensine and were decreased by the DAergic antagonist haloperidol and by the inhibitor of catecholamine synthesis alpha-methyl-para-tyrosine. It is suggested that the effects of AT II on open field behavior are realized through specific AT II receptors and through interactions with catecholaminergic (mainly dopaminergic) neurotransmission in the brain.

GABAergic influence on the effects of elymoclavine on exploratory behaviour of rats in open field.

The GABAergic influence on the effects of the ergot alkaloid elymoclavine on exploratory behaviour of rats in open field was studied using pharmacological tools. GABA was found to reduce the elymoclavine-stimulated exploratory behaviour. The GABAergic antagonists picrotoxin and bicuculline reversed the influence of GABA on the elymoclavine effects. The indirect GABA mimetics nipecotic acid, aminooxyacetic acid, di-n-propylacetate and semicarbazide also reduced the behavioural effects of elymoclavine. The data suggest some role of different functional states of the GABA system and of the close relationship between GABA and DA in the brain in the effects of elymoclavine on exploratory behaviour.

Central effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) in mice.

The central effects of endothelin-1 (ET-1, 0.5, 1, 2.5 and 10 pmol/mouse) and endothelin-3 (ET-3, 2.5, 5, 10, 20 and 25 pmol/mouse) have been studied after intracerebroventricular (i.c.v.) administration in mice. The following methods were used: behavioral observations, rotarod, spontaneous and amphetamine-stimulated motor activity, and hexobarbital-induced narcosis. ET-1 and ET-3 evoked a dose-dependent behavioral syndrome with a short excitatory period in the higher doses lasting for 5-10 min, followed by a prolonged depressive phase (about 90 min). ET-1 and ET-3 produced central depressive effects demonstrated by depressive behavior signs, decrease of the spontaneous and amphetamine-stimulated motor activity, and prolongation of the hexobarbital-induced narcosis.

Anti-hypoxic effect of centrally and systemically administered prostacyclin (PGI2).

Prostacyclin (PGI2) induced a dose-dependent prolongation of survival time of mice subjected to hypoxic and anoxic hypoxia, when administered either intracerebroventricularly (i.c.v., 0.001-10 micrograms/mouse), intravenously (i.v., 0.5-500 micrograms/kg) or intraperitoneally (i.p., 50-500 micrograms/kg). The effects of a single dose of 50 micrograms/kg i.v. or i.p. and of 1 microgram/mouse i.c.v. persisted for about 30 min. The anti-hypoxic effect of PGI2 is most likely due to an action upon the CNS.

Effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on convulsive seizures.

Endothelins (ET-1 and ET-3) are produced in the brain and may act as neuropeptides. The effects of two endothelins (ET-1 and ET-3) were investigated using pentylenetetrazole- (PTZ), strychnine- (STR), picrotoxin- (PIC) and bicuculline-induced (BIC) convulsions. ET-1 did not exert any anticonvulsive effect. ET-3, being more specific for the brain, showed anticonvulsive activity on PTZ and BIC seizures, but not on PIC and STR seizures. Different mechanisms underlie the action of the convulsants. PTZ, BIC and PIC realized their convulsive effects through the GABAergic inhibitory transmitter system; STR exerted an excitatory effect on the spinal cord by blocking the glycine transmitter system. The results suggest that the anticonvulsive effects of ET-3 might be due to an indirect influence on the GABAergic system in the brain.

Effect of CDP-choline on learning and memory processes in rodents.

The effects of cytidine (5') diphosphocholine (CDP-choline) on learning and memory were studied using conditioned reflex methods for passive avoidance and active avoidance with punishment reinforcement (step-through, step-down, shuttle box and maze), for active avoidance with alimentary reinforcement (staircase maze), and the Morris water maze. The majority of experiments involved comparative studies of the nootropic drugs meclofenoxate and/or piracetam. CDP-choline was administered orally, in some of the experiments also intraperitoneally, at doses of 10-500 mg/kg body weight once or twice daily for 5 or 7 days. In separate cases only single doses were administered. Trainings started one hour after the last dose of the drugs. Retention tests were given 3 h, 24 h, 7 days or 10 days after training. The results obtained with the different methods document CDP-choline's ability to improve learning and memory in rats and mice. No essential differences in the effects of CDP-choline were established upon oral and intraperitoneal administration of the drug. The learning- and memory-facilitating effects of CDP-choline were similar to those of meclofenoxate and piracetam. The results of the present study permit us to define CDP-choline as a substance capable of improving cognitive levels.

Influence of carbamazepine-10,11-epoxide on the serum level of valproic acid in epileptic patients on combined treatment with carbamazepine and valproic acid.

INTRODUCTION: Possible drug interactions in comedication have been the focus of intensive studies in the last decade. Polytherapy is often resorted to in epilepsy, and then the effect of factors such as gender, age, and metabolism should be taken into consideration. In this country, the anticonvulsant drugs used very frequently in a combined treatment of epilepsy are carbamazepine (CBZ) and valproic acid (VPA). The effect of CBZ is determined by the presence of its active metabolite carbamazepine-10.11-epoxide (CBZ-E) in blood serum. AIM: The purpose of the study was to find whether CBZ-E has any effect on the VPA serum level and whether this effect is age-dependent. MATERIAL AND METHODS: Blood samples from 52 epileptic patients on comedication with CBZ and VPA aged 3 to 53 years were examined. The patients were allocated into four age groups: preschool age (from 3 to 6 years)--9 patients; school age (from 7 to 14 years)--8 patients; adolescence (from 15 to 18 years)--11 patients, and adults (from 19 to 53 years)--24 patients. The serum levels of CBZ, CBZ-E, VPA were determined by gas chromatography. The ratio CBZ-E/CBZ of every patient was calculated. RESULTS: The CBZ and VPA levels we found were within the limits of their respective therapeutic ranges. The mean values of the serum level of the two drugs showed no statistically significant difference in the four age groups. In the school age group the mean values of CBZ and VPA were the lowest compared to the other age groups. CONCLUSIONS: The effect of CBZ-E serum level upon VPA serum level is age-dependent. In preschool age VPA manifests itself as inhibitor of CBZ-E metabolism. The ratio CBZ-E/CBZ does not affect the VPA serum level in combined therapy with these two drugs.

Effects of low-intensity electromagnetic fields on behavioral activity of rats.

The present study aimed at comparative assessment of the changes in behavioral activity of rats after exposing them to low intensity electromagnetic fields (EMFs) in the meter, decimeter and centimeter ranges. The experiments were carried out on 24 Wistar rats divided into 4 groups (1 control and 3 experimental), treated with different EMFs. The rats were irradiated on the head area at power density of 10 mW/cm2. Using a conventional shuttle box, the conditioned and non-conditioned responses and spontaneous motor activity of the rats were studied. The results suggest that exposure to EMFs in the three ranges can slow down the formation of conditioned responses--this was clearly marked in the rats exposed to meter EMFs, whereas the effects of centimeter EMFs were delayed in time. The behavioral effects were mild at athermal dosages and the animals adapted easily to exposure conditions. This study shows that determination of the effects of different EMFs should be done for each of the ranges separately; determination of the exact dosage of the electromagnetic fields can help to avoid their negative biological effects.